Fixup dup pip (#389)

examples/persistence_postgres.ipynb

@@ -42,7 +42,7 @@
    ],
    "source": [
     "%%capture --no-stderr\n",
-    "%pip install install --quiet -U langchain langchain_openai tavily-python langchain-postgres"
+    "%pip install --quiet -U langchain langchain_openai tavily-python langchain-postgres"
    ]
   },
   {